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Zhc Tftniversit^ of Chicago 

FOUNDED BY JOHN D. ROCKEFELLER 



THE LATERAL LINE SYSTEM 



OF 



BATRACHUS TAU 



A DISSERTATION 

Submitted to- the Faculties of the Graduate Schools of Arts, 
Literature, and Science, in candidacy for the degree of 

DOCTOR OF PHILOSOPHY 

(Department of Zoology) 
May, 1896 



BY 



CORNELIA MARIA CLAPP 



BOSTON, U.S.A. 

GINN & COMPANY, PUBLISHERS 

C&e ^tfjenaeum Press 

1899 



£be iftniversit? of Cbicaoo 

FOUNDED BY JOHN D. ROCKEFELLER 



THE LATERAL LINE SYSTEM 



OF 



BATRACHUS TAU 



A DISSERTATION 

Submitted to the Faculties of the Graduate Schools of Arts, 
Literature, and Science, in candidacy for the degree of 

DOCTOR OF PHILOSOPHY 

(Department of Zoology) 
May, 1896 



BY 



CORNELIA MARIA CLAPP 



* TV 

Zazf 







BOSTON, U.S.A. 
GINN & COMPANY, PUBLISHERS 

1899 



THE LATERAL LINE SYSTEM OF BATRACHUS 

TAU. 

CORNELIA M. CLAPP. 



CONTENTS. 



PAGE PAGE 

Introduction 223 Innervation 232 

General Considerations 237 

I. Adult Form. 

General Description 225 IL Larval Forms. 

Topography of the Lateral Line Origin of the Lateral Line System 238 

System 226 (1) Lateral line sense organs 238 

(1) Infraorbital line 226 (2) Lateral line nerves 242 

(2) Supraorbital line 227 (3) Formation of canals 244 

(3) Operculo-mandibular line 227 (4) Connecting strand 245 

(4) Body lines 228 Comparison with other teleosts 249 

Canals 228 Comparison with ganoids 250 

(1) Pores 229 Comparison with selachians 25O' 

(2) Relation of canals to cranial Comparison with dipnoids 250. 

bones 230 Comparison with cyclostomes 250 

Number and position of organs 231 Comparison with Amphibia 251 

Variations 232 General Summary 251 



Introduction. 

In a recent contribution to the " Skin and Cutaneous Sense 
Organs of Teleosts," Leydig (1) says: "Every one who has 
worked in this field shares the conviction that there is need 
of the cooperating participation of many observers before any 
conclusive presentation of the subject is possible." 

As the discoverer of the true nature of the so-called " lateral 
line " of fishes, Leydig's words have weight, when, after nearly 
fifty years of investigation, he is obliged to confess that " the 
points still obscure outnumber by far those well ascertained." 

Kupffer maintains that we are still on the very threshold of 
a history of the development of the peripheral nervous system. 
It is therefore the task of the investigator to furnish data for 
the future work of generalization. 



224 CLAP P. [Vol. XV. 

In the following pages an attempt has been made to describe 
the lateral line system of the toadfish, both in the adult and 
developmental stages, for, as Mr. Allis (2) has well said, the 
"purely descriptive part of the subject" has been too much 
neglected. 

Frequent reference will be made to the conditions existing 
in Amia, and the nomenclature employed by Allis will be 
adopted. 

Ryder (3) describes the appearance of the lateral line organs 
in the young toadfish at the time of the formation of canals on 
the head, and speaks of the lines of free organs on the body 
as canals/ It is evident that his observations, though in many 
ways valuable, were incomplete. So far as I am aware, this 
preliminary "notice" contains all we have on the subject of 
the lateral line system of the toadfish. 

In Jordan's "Synopsis of Fishes of North America" (4) the 
only mention of this system is the statement that in Batrachus 
there is "710 lateral line, nor conspicuous pores." 

My study of the lateral line system of Batrachus was begun 
in the summer of 1888, under the direction of Prof. C. O. 
Whitman, at the Marine Biological Laboratory of Woods Holl, 
Mass., and completed at the University of Chicago. 

I wish to express my deep feeling of obligation to Pro- 
fessor Whitman for the interest he has taken in the supervi- 
sion of my work ; and for the many courtesies and suggestions 
received from instructors and associates, I wish here to make 
.acknowledgment. 

For assistance in obtaining material at Woods Holl I am 
greatly indebted to Mr. G. M. Gray, the Collector of the 
Marine Biological Laboratory ; for specimens of Acanthias I 
wish to thank Dr. A. D. Mead and Prof. A. D. Morrill. 

The drawings for this paper were made after my sketches 
by the following draughtsmen at the Marine Biological 
Laboratory : 

Figs. 1-3 and 7-1 1 were made by Mr. Crosby. 
" 4-6 " " " Mr. Tokano. 

"12 « « « Mr. John Walton. 

" 22, 23, 24 « « « Mr. Hayashi. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 225 

I. Adult Form. 

General Description. 

There is something singularly grotesque in the appearance 
of the toadfish ; and, as its name would imply, there is a 
superficial resemblance to the familiar batrachian. The slug- 
gish disposition, the mottled brown and gray of the wrinkled, 
scaleless skin, the depressed head and toadish eyes do not 
suggest the typical teleost. The young fish also are tadpole- 
like in their form and motions. 

From PL XVII, Figs. 1-3, it will be seen that there are quite 
conspicuous projections of the skin on the head. Besides the 
paired flaps found in connection with the sense organs, there 
are other single, often longer projections to be found, which 
become laciniated in the older fish. These are especially 
prominent about the mouth, fringing the margin of the lower 
mandible and opercular regions, while over each eye rises a 
broad conspicuous flap, giving an owl-like facial expression. 
The goosefish (Lophius) and the sea raven (Hemitripterus) 
.also possess these somewhat ornamental appendages about the 
mouth. The function of these skinny tentacles seems evidently 
to be for protection, as they strikingly resemble both in color and 
form the seaweed (fucus) that abounds near their favorite haunts. 

The toadfish frequents the shallow water of bays and inlets 
of the sea, ranging on the Atlantic coast from Cape Cod to 
Florida. 

It is abundant at Woods Holl, Mass., and is easily obtain- 
able in the month of June, during the spawning season. At 
this time the fish resort in pairs to large stones, usually near 
low watermark, and scooping out a cavity beneath, remain for 
days in their retreat. The toadfish of the Eel pond near the 
laboratory seem to prefer the debris of civilization to the 
excavation beneath the rock ; for example, tin cans, old boots, 
broken jugs, etc. After depositing the eggs, the female 
departs, while the male remains to guard the nest. 

The young fish do not " attach themselves by a ventral disc 
which soon disappears," as has been supposed, but at the time 



226 CLAP P. [Vol. XV. 

of oviposition each egg is securely glued to the rock by means 
of a secretion on the egg membrane at the pole of the egg 
opposite the micropyle. 

After hatching, the embryo fishes still remain attached to 
the rock by the adhesion of the yolk sac to the inside of the 
egg membrane over the disc area, until the yolk material 
has been entirely absorbed — a period of three or four 
weeks. 

The largest toadfish seldom reaches a length of more than 
twelve inches. 

Dr. Goode (5) gives the following facts about the toadfish : 
" In general appearance it resembles a sculpin. It possesses 
the power of changing its color to lighter or darker shades 
when exposed to light in shallow vessels with dark or light 
colored bottoms. It probably becomes torpid in winter in the 
more northern regions, is very hardy, and utters a loud croaking 
sound when handled." 

In Storer's description of Batrachus tau one finds certain 
statements which are hardly correct. For example, he speaks 
of the eggs as being " not larger than very small shot," as 
" increasing in size " after deposition, also as adhering by a 
" disc acting as a sucker," and finally he says of the fish which 
remains to guard the eggs, that " it is in all cases the mother 
of the young ones." 

Topography of the Lateral Line System. 

1. Infraorbital line. — The first six organs of this line are 
found on a semicircular fold of the skin, anterior to the nasal 
tube (PL XVII, Fig. 2). These organs constitute the antorbital 
portion of the infraorbital line. They are free organs pro- 
tected by a pair of flaps of the skin, representing in their posi- 
tion the sides of a canal. Each organ occupies a depression in 
the skin, and on opposite sides are developed the pointed flaps 
which arch over this depression, the tips of the flaps almost 
meeting over the center of the organ (Fig. 1). 

There is no anterior commissure between the infraorbital 
lines of the two sides of the head as seen in Amia. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 227 

At a point midway between the anterior and posterior nares 
the infraorbital line branches. One division extending along 
the border of the maxillary may therefore be called the maxil- 
lary branch, the other being the suborbital portion of the main 
line (Fig. 1). There are seven organs in this maxillary branch, 
five being free organs and two enclosed in a short canal 
(PL XX, Fig. 22). The suborbital portion consists of eight 
free organs, bordering the lower half of the orbit (Figs. 22 
and 23). 

At the outer angle of the eye there are two free organs 
(9, 10) continuing the line of the infraorbital and correspond- 
ing to the otic portion (15, 16) as seen in Amia. (Compare 
PI. XX, Figs. 21 and 22.) In the temporal portion of the line 
there is a single organ (11) enclosed in a canal (Fig. 22). The 
infraorbital line is continued on to the body as the dorsal line 
of free organs (Figs. 22 and 24). 

2. Supraorbital line. — There are seven organs in this line. 
The first, a free organ, is situated near the median line, a little 
anterior to the opening of the posterior nares (PL XX, Fig. 22). 
Organs 2-6 are enclosed in a canal, while the seventh is a free 
organ occupying a position apparently outside the line and on 
the top of the head (PL XVII, Fig. 2 ; PL XX, Fig. 22). There 
is evidence of the presence of the supra-temporal cross-commis- 
sure, although the canal seen in Amia is wanting in Batrachus. 
In one specimen, 12 cm. in length, the line was conspicuous, 
as two extra organs were present in this region of the head. 
In PL XX, Fig. 22, st.com. , the position of the line is indicated. 
The middle pit line of Amia may be represented in Batrachus 
by the organ just dorsal to the temporal canal (Fig. 22, m.l.). 

Four organs on the top of the head, extending on to the 
trunk each side of the first dorsal fin, constitute what is desig- 
nated by Allis as the dorsal body line in Amia. (Compare 
Figs. 21-23.) 

3. Operculo-mandibular line. — The first organ of this line is 
found on the lower side at the symphysis of the mandible. 
There is no commissural connection here between the two 
sides of the head. Four organs, which never become enclosed 
in a canal (Fig. 3), occupy a depression which appears as an 



228 CLAP P. [Vol. XV. 

open groove in the bone (Fig. 5). The succeeding organs, 
5-7, are within a canal in the articular bone (Fig. 5). At the 
angle of the jaw the opercular division begins, and consists of 
four enclosed organs (8-1 1) with one (12) free organ near the 
temporal region (Fig. 22). Outside of these twelve organs of 
the operculo-mandibular line there are accessory lines of free 
organs. On the mandible there is a short line of three organs 
(PI. XVII, Fig. 3, ac.md.l.) anterior and parallel to the canal. 
Near the pore at the junction of the two portions of the 
operculo-mandibular line there are two free organs (mdl.) (Figs. 
1, 3, and 22), while on the operculum two lines of free organs 
diverge at right angles to the canal in the preoperculum, the 
more dorsal (d.o.l.) having four, and the other (v.o.l.) three 
organs (Fig. 22). 

4. Body lines. — There are three lines of free organs on the 
side of the body (Fig. 24) ; the most dorsal, of twenty-seven 
organs, being a continuation of the infraorbital, the middle line 
appearing as a branch from this line, represented by only a few 
scattered organs, usually eleven, and the ventral line, of twenty- 
seven organs, extending from a point in front of the ventral 
along the border of the anal fin. Continuations of these lines 
are found on the caudal fin, but the organs are somewhat 
diminished in size toward the posterior end of the body. The 
usual number on the caudal fin is four. 



Canals. 

The canals enclosing lateral line organs are found only on 
the head, and these present a rudimentary, perhaps vestigial 
condition in Batrachus. 

From Fig. 22 it appears that the infraorbital line through- 
out its extent has only two short canals, one on the maxillary 
branch containing two organs, and the other in the temporal 
region enclosing only one. The supraorbital line, on the other 
hand, exhibits the opposite condition, in that all the organs of 
the line are enclosed in a canal with the exception of a free 
organ at each end of the line. The operculo-mandibular canal 
is well developed, only five of the twelve organs being super- 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 229 

ficial. There is a direct union of the canals of the two sides 
of the head between the eyes, but no organ is developed in 
this commissural portion (Fig. 23 ; also Fig. 4). 

Pores. 

For a complete understanding of the relation of the pores 
to the canals, a knowledge of their mode of development is 
necessary. Each organ becomes enclosed in a short canal 
(Cut 1), the two openings of which are called by Allis terminal 
or half pores. By the union of these half pores, the so-called 
primary pores of the young Amia are formed. 

In the case of Amia there is a subsequent process of division 
of these primary pores, resulting in the dendritic systems of 
the adult fish. The pores in Batrachus correspond to the 
terminal and primary pores of Allis, as shown in the diagram 




«, 





_fL 



Cut i. — Diagrammatic representation of the formation of a primary pore : a, B, and c, two 
terminal pores approaching each other and fusing ; d, primary pore. 

representing the post-larval stage of Amia. (Compare Figs. 
21 and 22.) In the supraorbital line of Batrachus the primary 
pores have become fused, so that only the two terminal pores 
are present, and no pore marks the union of the canals between 
the eyes, as seen in Cottus gobio. These pores, in process of 
fusion, may be observed during the development of the canals 
in the young fish. 

It seems all-important that the term pore be restricted in its 
application to the openings into the canals. In consequence of 
the indiscriminate use of this word, it is often difficult to under- 
stand the statements of some writers. A puzzling case is pre- 
sented in a description of the canals of Polyodon by a writer (6) 
on the Sensory System of Ganoids, where the " cluster pores " 
are described as openings of canals, and figured as sense organs ! 

A recent writer (7) in alluding to this subject says: "The 
word pore is inappropriate in Amphibia if used in the same 



230 CLAPP. [Vol. XV. 

sense as in fishes," as may be easily understood when it is 
known that no canals exist in the Amphibia. 



Relation of Canals to Cranial Bones. 

From an examination of the skull (Fig. 4) it appears that 
grooves or open channels in the bones serve as protection 
for the organs. In Batrachus the only cranial bones which 
become modified to give protection to the lateral line organs 
are the frontal, dentary, and articular bones, the preoperculum, 
and an accessory membrane bone in the maxillary branch of 
the infraorbital. The curious T-shaped arrangement of the 
upper surface of the frontal bones where the canals of the two 
sides of the head unite, has given the specific name (tau) to 
the species under consideration. These channels are spaces 
between ridges of bone projecting from the surface and 
partially surrounding the membranous tube containing the 
sense organs. They vary in diameter in the different regions 
of the head. In the opercular region this membranous tube 
occupies the space (Fig. 4) between the outer edges of the 
two lamellae of bone forming the preopercle. In the canal 
of the maxillary branch the accessory membrane bone appears 
as though folded together to enclose the canal (Fig. 4, ac.b.). 
In the mandible there is the nearest possible approach to a 
closed bony canal (Fig. 5), while in the case of the temporal 
canal there is no cranial bone involved. This short canal lies 
outside the muscles which cover the squamosal and occipital 
bones, and consists of a tough fibrous or semi-cartilaginous 
covering within which is the lining epithelial layer (Fig. 22, 
T.C.). Leydig (8) figures a similar formation in Chimaera. 
The supporting substance is described as consisting of incom- 
plete rings, one behind the other, comparable to the rings of 
the trachea, and the free ends of these rings are represented 
as branching. In cross-sections of the temporal canal in 
Batrachus a very similar structure is seen. 

At the anterior end of the supraorbital canal there is a 
scale-like cartilaginous formation, by means of which the canal 
is extended across between the two openings (Fig. 2 2). of the 




No. 2.] LINE SYSTEM OF BATRACHUS TAU. 23 1 

nasal tube. This scale bears some resemblance to the carti- 
laginous tube of the temporal canal, yet is unlike it, and seems 
to be a peculiar structure found in no other part of the canal 
system of Batrachus. Something very similar is found in the 
canal of the trunk in Cottus gobio (Cut 2), 
as described and figured by Bodenstein (9). 
The nasal tube itself is a canal belong- 
ing to this system which never becomes 
surrounded by any bony formation. In cut 2. — scale from trunk 
this connection it may be stated that there 
is good reason for regarding the semicircular canals of the 
ear as belonging to the lateral line system, although shut off 
entirely from the surface of the body. This view has been 
advocated by Ayers (10) and other writers. 

Number and Position of Organs. 

In Batrachus the organs in canals are identical with the 
so-called free organs, the only difference being the fact that 
the free organs, being situated on dermal papillae, have a 
slightly different form. 

The number of organs on the head is 128, and on the body 
140, making a total of 268 organs on the entire surface of the 
head and body. The number enclosed in canals is only 30, 
making the number of free organs 238. There is no indication 
that the number of organs increases by multiplication during 
the life of the fish, and the "nerve ridges " described by Allis 
(2) have never been found in Batrachus. The " pit organs " of 
Amia, assigned to the same general class of nerve hillocks, 
are yet said to differ greatly from the canal organs in " shape, 
arrangement, and methods of multiplication." From the 
description, however, there seems little evidence of greater dif- 
ference than between the enclosed and free organs of Batra- 
chus, except, possibly, in the size. It seems quite impossible to 
arrange them in two separate groups in the case of Batrachus, 
as they replace so constantly the regular canal organs. The 
enclosure of organs within a canal seems quite incidental and 
secondary. The absence of accessory lines of pit organs is 



232 CLAP P. [Vol. XV. 

quite noticeable in Batrachus, as also the numerous " surface 
sense organs " (terminal buds) described by Allis (2) on the 
head of Amia. 

Variations. 

Frequent variations in the number and position of the organs 
have been noted. There may be five, six, or seven organs in 
the antorbital portion of the infraorbital line. The number 
in the suborbital may be eight or nine. In the mandibular 
line at the place of union of the opercular and mandibular 
divisions one organ is often wanting. 

Two extra organs — one on each side of the head — 
occurred in the case of one specimen, confirming the opinion 
that the free organs of this region are homologous with those 
of the commissural canal in the occipital region of Amia. 
(Compare Figs. 21 and 22.) 

On the body the variation is still more marked, the two sides 
seldom having exactly the same number or arrangement of 
organs. 

On one large specimen there was the following arrangement : 

In the dorsal body line of the right side, 25, left 29. 
" " middle " " " " " " 11, " 8. 
" " ventral " " " " " " 26, " 27. 

At the anterior end of the ventral line in another specimen 
one organ was lacking on each side. The number may be four, 
five, or six on the caudal fin. 

Innervation. 

The method most successfully employed for determining the 
course of the nerves was maceration of the adult fish in nitric 
acid. After being kept for some time in a weak solution, not 
only the large nerve trunks could be easily followed, but the 
bundles composing these trunks could be separated, the con- 
nective tissue sheath having been dissolved. It thus became 
possible to demonstrate the course of the different components 
of nerves enclosed in the same sheath. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 233 

By reference to the diagrams (Figs. 22 and 23) which represent 
the side and dorsal view of the head and anterior part of the 
body of an adult toadfish, the course of the nerves may be 
traced after their exit from the skull. Fig. 21 is reproduced 
from Allis's plate for purposes of comparison, as it is of interest 
to note the general resemblances and slight differences which 
appear in comparing the teleost Batrachus with the ganoid 
Amia. As may be observed, the number of organs in the 
different lines and their mode of innervation correspond in a 
surprising manner. 

The lateral line system in the head of Batrachus is innervated 
by dorsal branches of the VII and X cranial nerves. 

The VII Nerve. 

The supraorbital line is innervated by the R. ophthalmicus 
superfacialis facialis (Fig. 22). This branch arises from the 
ganglion lying above the Gasserian ganglion (Fig. 13), and 
runs along the inner margin of the orbit in close association 
with the ophthalmic branch of the trigeminus. There is 
an evident interchange of fibres in one place, and the two 
nerves are included in the same sheath for a short distance 
near their peripheral termination. Each organ is supplied by 
a short branch, which enters the bony canal immediately below 
the organ. Organ No. 7 being a free organ, and on the top of 
the head, yet belongs to this supraorbital line of organs, as 
may be seen by tracing its development and its innervation. 
As Allis has shown in Amia, the supraorbital line is widely 
separated, at an early period of development, from the infra- 
orbital, at the point where later there is a union of the two 
canals. 

Infraorbital line. — The organs in the pre-auditory part of 
the infraorbital line are innervated by the R. buccalis facialis 
(Figs. 22 and 23, buc.f.). This branch arises from the facial 
(Fig. 13), lying above the Gasserian ganglion, and immediately 
divides, sending a comparatively small number of fibres (Fig. 
13, buc.f?), to the outer angle of the orbit to supply the eight 
organs of the suborbital portion of the infraorbital. The 



234 CLAP P. [Vol. XV. 

main portion of the buccalis passes directly downward to the 
floor of the orbit (Fig. 13, due./. 1 ) enclosed for some distance 
in the same sheath with the maxillaris of the fifth. It then 
again divides, one branch being directed toward the median 
line supplying the six antorbital organs, while the other sends 
branches to the seven organs which constitute the maxillary 
portion of the infraorbital line (Fig. 23). The two organs 
(9, 10) of the infraorbital line, corresponding to those inner- 
vated by the otic branch in Amia (Fig. 21), are in Batrachus 
supplied by a branch from the R. buccalis facialis (Figs. 
22 and 23). 

Operculo-mandibular line. — The organs of this line are 
innervated by the R. mandibularis externus facialis. Organ 12, 
— a free organ, — together with the most dorsal of the two 
branch lines of free organs on the operculum (Fig. 22, d.o.l.), 
are innervated by a branch of the hyoideo-mandibularis facialis, 
before the externus has separated from it. It leaves the main 
trunk through the foramen at the base of the opercular 
spine. 

Organs 8-1 1 are supplied by branches which pass from the 
externus between the bony lamellae of the preoperculum to 
the canal occupying the space between the outer edges of these 
lamellae. Between organs 9 and 10 a branch is given off to 
the three free organs forming the ventral line on the opercu- 
lum (Fig. 22, v.o.L). 

There are two free organs situated near the large pore which 
marks the union of the opercular and mandibular portions 
of the line, and which seem to correspond to the mandibular 
pit line of Amia (Fig. 21, m.d.L), which are innervated by 
branches from the externus. In the same way the two free 
organs at the angle of the mouth in Batrachus may easily be 
identified with the vertical cheek line in Amia (Fig. 21, c.L) y 
also supplied by a branch from the externus. 

The three canal organs of the mandible are innervated by 
the externus, as also the four organs in the groove at the ante- 
rior part of the mandible (Fig. 3), while the three superficial 
organs in a line parallel with them are also supplied by a 
branch of this same nerve (Fig. 22, ae.md.l.). 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 235 

There seems to be an interesting peculiarity in the innerva- 
tion of the body lines of Batrachus. The N. lineae lateralis 
does not supply the line of sense organs continuous with the 
infraorbital of the head, but it does send branches to some of 
the scattered organs of the middle line. The dorsal and ven- 
tral lines of the body are innervated, in part at least, by the 
R. recurrens facialis. This nerve emerging from the ventral 
branch of the dorsal VII (Fig. 13) turns directly backward 
within the cranial cavity; it passes obliquely through the cranial 
wall and through a loop in the glossopharyngeal, beyond 
which it forms an anastomosis with an ascending branch 
from the posterior root of the vagus, at a point just behind the 
auditory capsule. The position of the R. recurrens facialis is 
superficial to the N. lineae lateralis, and it extends on to the 
body just underneath the skin. It divides immediately (Fig. 
22), sending one branch toward the dorsal region supplying 
the organs of the anterior portion of the dorsal line, while the 
ventral branch curves around behind the base of the pectoral 
fin innervating the anterior organs of the ventral line. 

The X or vagus nerve. — The anterior root of the vagus 
nerve arising from the dorsal region of the medulla (Fig. 12, 
X an.r.), does not possess any distinct ganglion. It runs 
backward and outward, crossing the main root of the vagus, 
with which it is connected by a few fibres, and after leaving 
the cranium by the foramen in the occipital is continued on 
the body as the N. lineae lateralis. It courses deeply under- 
neath the muscles for some distance, becoming superficial at 
the posterior portion of the body. 

Although this is the main lateral line nerve, it seems to 
innervate only a few of the organs on the body of Batrachus. 

The supratemporal branch of the vagus is composed mainly 
of anterior root fibres (Fig. 13, st.v. 1 ). It arises intracranially, 
passing upward and leaving the skull through a foramen in the 
supraoccipital (Fig. 4, o.c.f). It then turns forward, supplying 
the canal organ of the temporal region (Figs. 22 and 23) and 
three other organs on the top of the head. The most anterior 
of the three organs may be considered as representing the 
middle dorsal line of pit organs, which in Amia are innervated 



; ] f CLAPP. [Vol. XV 

branches of the IX, while the two others are probably 

homologous with the organs forming the cross-commissure of 
Amia. (Compare Figs. 21 and 21.) 

Another branch (v. 2 ), arising from the anterior root of the 
TOgns just outside the cranium, and taking a course upward and 
backward, innervates the four organs of the dorsal line (Fig. 
::. dl.). 

Fig. 13 shows an intracranial commissure between the VII 
and X. The branch from X which anastomoses with the R. 
recurre-s :i::il:= Fig. 13) arises from the posterior root of the 
TOgns. It is also evident that the fibres of the R. recurrens 
facialis emerge with the ventral root fibres of the VII. It is 
probable that the components of this nerve have a different 
central terrnination in the medulla from the dorsal branches 
of the VII and the anterior root of the X. The innerva- 
tion of the body lines in Batrachus presents a somewhat 
puzzling problem, which can only be solved by a careful study 
of the terminations or origin of the fibres in the medulla. The 
apparent course of the nerves is often deceptive, as fibres hav- 
ing different central connections are enclosed in the same sheath 
outside of the medulla, or, the central connections being the 
7 :he fibres follow different pa:. :o their destination. 

A case in point is that of the glosso-pharyngeal, which seems 
to take no part in the innervation of sense organs in Batrachus, 
although in Amia one canal organ and a line of pit organs are 
supplied by that nerve. 1 It is probable that the fibres inner- 
TOling the organs are enclosed sometimes with the IX and 
s:r_;t rimes with the X nerve 

The attempt to homologize the body lines of Batrachus 
seems useless until a better knowledge of the components of 
the so-called R. recurrens facialis is obtained. It seems prob- 
able that this nerve is identical with the R. dorsalis recurrens 
ti%emini (Stannius), which is said to innervate a line of end 
tads at the base of the dorsal fin in Siluroids, but the dorsal 
body line of organs in Batrachus would hardly seem homologous 
with this line of end buds. 

- L: 1 r~:~--. y~z<i: Journal of Morphology - :. x_ r "_- . 1 „— : : i- si:~~ 
daft the -"so-called dorsal root " of the IX is composed of fibres from tit la.tr ral 
Jne root of X. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 27,7 

General Considerations. 

If one may judge from the contributions to this subject by 
various investigators, it is becoming evident that the lateral 
line system may take rank among the organs of special sense. 

The connection of the olfactory, optic, and auditory organs 
with the central nervous system is effected by means of special 
pairs of cranial nerves originating in definite centers within the 
brain. On tjie other hand, the sensations of touch are medi- 
ated by cutaneous nerves which seem to be so universally dis- 
tributed as to suggest the idea that the skin itself may be 
regarded as an immense sense organ and its innervation corre- 
spondingly general. 

The system of the lateral line has usually been regarded as 
composed of organs of the more generalized type. Their wide 
distribution over the entire head and body would favor this 
conclusion, but the study of the cranial nerves of Amphibia 
brings into view several significant facts. In his recent paper, 
Strong (n) calls attention to a "most beautiful extirpation 
experiment in nature." The tadpole has the sense organs 
found in fishes and the Urodeles, and these organs are inner- 
vated by certain dorsal branches of the cranial nerves. When 
the tadpole becomes a frog, and these organs disappear from 
the skin, the dorsal branches supplying them become atrophied. 
As regards the innervation of the lateral line organs, there 
seems to be a remarkable agreement between the Urodela, larval 
forms of Anura, and the fishes. In general, the arrangement 
seems to be the same, inasmuch as dorsal branches of the VII 
and X cranial nerves supply these organs. This has been 
shown in the case of amphibians (n), selachians (12), two 
ganoids and one dipnoid (13), but among teleosts the mat- 
ter has been in doubt. Batrachus is certainly one teleost in 
which the dorsal branches are present and innervate the lateral 
line organs. 

In his analysis of the cranial nerves of Amphibia, Strong 
gives a description of the different nerve components distin- 
guishable by the nature of their fibres, peripheral distribution, 
and internal origin. 



2 ; S CLAP P. [Vol. XV. 

He describes a general cutaneous component and a special 
cutaneous or lateral line component, the dorsal branches of 
which innervate the organs of the lateral line. These branches 
are coarse fibered and therefore distinguishable in sections, 
while their internal origin or termination is the tuberculum 
acusticurn, a portion of the medulla which is greatly developed 
in fishes. If the lateral line component has its origin in the 
tuberculum acusticurn, we have good reason to conclude that 
the localization of function in the medulla is as definite for 
these widely distributed organs as it is for the more circum- 
scribed patches of sensory epithelium seen in the case of the 
ear, eye, or olfactory organ. 

The ear furnishes a fine illustration of this subject, and seems 
like a connecting link between the system of lateral line 
organs from which it has probably originated, and the most 
highly modified sensory structure in Vertebrates — the eye 
Ayers (10) has shown that the auditory organ is in reality a 
series of canal organs innervated by two distinct cranial 
nerves which he regards as possibly dorsal roots of VII and IX. 

II. Larval Forms. 

Origin of tJie Lateral Line System. 

I. Lateral line sense cigans. — Sections of early stages in 

the development of Batrachus show thickenings of the ectoderm 
in the region behind the eyes. In sections of later stages these 
areas of thickened ectoderm have become invaginated to form 
the auditory vesicles. Immediately after the closure of the 
auditory pits, thickenings of the lower layer of the ectoderm 
are observed on each side of the head in the pre-auditory region. 
From this thickened area two cords extend, one above and 
another below the eye. These cords are the rudiments of the 
supraorbital and infraorbital lines of sense organs. 

Simultaneously in -the post-auditory region there appear 
similar thickenings of the ectoderm which extend rapidly 
backward on to the trunk. In very young embryos this line 
advances along the side of the body with an enlargement at the 
growing end. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 239 

These thickenings of the ectoderm are described by H. V. 
Wilson (14) as " sensory tracts," and he maintains that in the 
bass, unlike what has been observed in selachians, in Amia 
and in the trout, the lateral line originates in the form of 
"sensory sacs," which later on become flattened out into the 
" patches " described by other authors. There is no dissent 
from the view that the auditory region is the place where the 
lateral line system originates, but the occurrence of these 
"sensory sacs" appears to be peculiar to the bass. Wilson 
states that the ear, branchial organ, and the first of a series of 
organs extending on to the body, are derived from this " common 
sensory furrow." In Batrachus there is no definite furrow 
present, and the "branchial sense organ" described as "func- 
tional in the later stages of embryonic and during larval life " 
is certainly not "histologically differentiated" as in the bass. 
There is no sign of an organ composed of " sense cells with 
short stiff hairs," as described by Wilson in an embryo of 
fifty-nine hours. 

Fig. 17 shows the growing end of this line as seen in a 
preparation of the skin of an embryo 5 mm. in length. After 
fixing in picro-sulphuric acid and slight maceration in water, 
if the skin is removed, stained in alum cochineal, and mounted 
in glycerine, the proliferating cells in the lower layer of the 
ectoderm may be clearly seen. A horizontal section of this is 
shown in Fig. 18, at the time when the growing point has 
reached only a short distance behind the pectoral fin. A 
more highly magnified view of a portion of the same is seen in 
Fig. 19. A comparison of the lateral line of Batrachus at 
this stage with the same structure in an Acanthias embryo is 
of interest (Fig. 14). In Acanthias the lateral line is quite 
conspicuous. In an embryo of 22 mm. (Cut 3) it is easily seen 
with a hand lens, as a prominent, somewhat flattened ridge, 
extending backward above the branchial region and along the 
sides of the body. There is a curious fold of the epidermis, 
the so-called " pocket," which covers the growing end of the 
line. PI. XIX, Fig. 14, shows a horizontal section of an embryo 
17 mm. in length, from which it is evident that the "pocket" 
consists of a reduplicature of the skin accompanying the 
enlarged growing point. 



240 



CLAP P. 



[Vol. XV. 



The branches of this system on the head also show this 
peculiar fold (Cut 3), the significance of which it is hard to 
discover. In connection with this fold, Mitrophanow (15) 
describes the formation of canals, but gives no figures that 
illustrate the manner of their formation. Behind the dorsal 
fin, as seen in older embryos, the " pocket" becomes greatly 
elongated, and suggests the existence of a canal in that region, 
but furnishes no clew to the condition that is supposed to exist 
in the anterior part of the body of the adult Acanthias. Cut 
4 is a cross-section of the anterior part of the line at this stage. 




Cut 3. — Acanthias embryo, 22 mm. in length 



This subject has not been sufficiently investigated to afford a 
satisfactory basis for comparisons. Beard (16) mentions this 
growing end of the line as " plowing its way backward through 
the indifferent ectoderm." The appearance of the structure 
in Acanthias would suggest this idea. 

Balfour (17) describes the lateral line of Syllium as appearing 
^ in the form of a linear thickening of the inner row of cells of 
the external epiblast on each side, at the level of the notochord." 
He says that at this time it shows no segmental character, and 
he also notes the interesting fact of the "broadening at the 
growing point." He probably has reference to this remarkable 
fold of the epiblast when he speaks of the "perfectly abrupt " 
termination of the line. He also mentions the contrast between 
the narrow anterior and the broad terminal portion of the line. 
This thinning out of the anterior portion of the lateral line is 
noticeable in Batrachus. Allis describes and gives figures of 
surface preparations showing the same appearance of the line in 
Amia. " The ends of these lines are enlarged, that of the 
lateral line sometimes forming a large and prominent swelling." 

Hoffmann (18) regards the sense organs as arising seg- 
men tally, and gives no account of the growth of the rudiment 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. , 24 1 

of sense organs on the side of the body. H. V. Wilson (15) 
has evidently found the line only in the form of a slender cord 
on the posterior part of the body, and makes no mention of 
any enlargement at the growing end. From figures in a 
recent paper on Necturus, by Miss Piatt (19), this enlarged 
growing point is shown as quite conspicuous. In selachians, 
ganoids, and amphibia we have evidence of this mode of 
growth of the sense organ rudiment, but no figures or descrip- 
tions of the enlarged growing point of the lateral line of any 
teleost have been published, so far as I am aware. 

Fig. 6 represents the condition of a Batrachus embryo 
about the time of hatching and when the embryo is still 
attached to the yolk sac. The principal organs of the different 
lines can now be distinguished in surface preparations, but a 
more satisfactory showing of the exact number and position of 
the organs, as well as of the connecting strand, can be obtained 
from preparations of the skin, as previously described. 

Regarding the canal and free organs as identical, the devel- 
opment may be briefly outlined as follows : In Batrachus, as 
in Amia, the growing line of sensory epithelium begins to 
present the appearance indicated in Fig. 1 5, which is a camera 
drawing from a preparation of the skin at a stage somewhat 
earlier than that shown in Fig. 6. The cells destined to 
form the sensory portion of the organ begin to elongate and 
arrange themselves in a definite manner, suggesting the name 
"hillock" given by Merkel (20) to this class of organs. At 
the summit there soon appears a clear vacuolar space toward 
which the upper portion of the cells is directed. The 
"hillock" formed in the lower layer of the skin soon pushes 
its way to the surface and gradually takes on the characteristics 
of an adult organ. This process has been fully described by 
Allis (2). 

The sensory and supporting cells are very much alike in the 
organs of Batrachus, although the cells in the center of the 
"hillock" are pear-shaped and somewhat shorter than those 
of the peripheral part of the organ. From Fig. 16, which is a 
section of a side organ of a fish of one year old, the shape of 
the adult organ is evidently that of a cone hollowed at the base. 



242 CLAPP. [Vol. XV. 

Soon after the organ has reached the surface, there appears 
on the summit a structure known as the " hyaline tube" or 
" cupola." This was seen on specimens 2 cm. in length, being 
easily observed with low magnifying power on the living fish, 
some chloroform being added to the water to quiet the fish 
during the observation. This tube measured .10 mm. in length 
and .01 in breadth. From sections through the canal organs of 
older fish, it is apparent that this " hyaline tube" is present 
after the enclosure of the organs in canals. There is little 
doubt in regard to the nature of this hyaline structure. The 
cells of the organ, in common with other epidermal cells, may 
secrete a cuticular substance on the free ends of the cells. In 
the case of the hair cells this secretion is in the form of hairs 
or bristles. These hairs may coalesce, forming a continuous 
membrane, surrounding the central portion of the hillock, 
thus forming the so-called tube, which is frequently present. 
The hairs of the most central cells may remain separate within 
this tube, as Leydig (1) observes in his most recent paper on 
this subject. 

The " terminal buds" of Merkel or "end buds" of other 
writers are not found on the surface of the head or trunk of 
Batrachus, but they occur in the mouth and branchial cavities. 
These organs are much smaller than the hillocks on. the surface 
of the body, and very little is known in regard to their 
innervation. 

2. Lateral line nerves. — In his " Elasmobranch Fishes " Bal- 
four (17) says that, in considering the subject of the lateral line 
system, we are dealing with two distinct structures, (1) the 
modified epidermis seen in certain lines along the sides on 
the head and body, and (2) the accompanying nerves. 

The origin of the organs from the modified ectodermal cells 
has been demonstrated, but the mode of origin of the accom- 
panying nerves is not so well understood. Balfour (17), follow- 
ing what he believed to be the analogy of cranial nerves in 
general, held that the dorsal branches which supply the sense 
organs grow out from the brain to these organs. On the other 
hand, Gotte (21), Semper (22), van Wijhe (23), and Beard (16) 
consider it certain that the cells from the ectoderm contribute 



No. 2.] 



LINE SYSTEM OF BATRACHUS TAW. 



243 



//r.-« 



to the formation of these branches. According to Hoffmann 
(18), the lateral nerve in Salmo arises from a string of cells in 
the nervous layer of the ectoderm some time previous to the 
development of the organs. This string gradually moves out 
of the ectoderm, coming to lie at some distance internal to it, 
but connected at intervals 
by short side branchlets with 
the locality where the future 
segmental sense organs are 
to arise. Hoffmann's (18) 
observations were made on 
embryos of a teleost, which 
he regards as a less favor- 
able form than the selachian, 
in which, according to Sem- 
per (22), it is uncommonly 
easy to show the origin of 
the lateral nerve. 

In the section of the 
Acanthias embryo (Fig. 14), 
there is an evident exten- 
sion of nerve fibres from 
the vagus ganglion accom- 
panying the lateral line 
rudiment. In cross-section 
these fibres are seen to con- 
stitute at this stage a part 
of the lateral line (Cut 4). It will be necessary to study the 
changes taking place in the later stages before a final conclusion 
can be drawn, but it would appear that the thickened ectoderm 
forming the lateral line and the extension of the outgrowths of 
the ganglion cells were associated during the early history 
of the structure. 

Hoffmann's (18) description of the origin of the nerve 
becomes more intelligible after the study of the selachian 
embryo, although in both the case of Salmo and Acanthias the 
exact mode of origin of the sense organs remains uncertain. In 
Batrachus, on the other hand, the origin of the sense organs 




Cut 4. — Cross-section of lateral line of 
Acanthias embryo. 



244 CLAPP. [Vol. XV. 

is easily demonstrated, while the origin of the nerves arid their 
connection with the organs becomes the great problem, as in the 
case of other teleosts. 

In stages represented in Fig. 18 it is impossible to detect 
any nen'e fibres accompanying the growing line on the side 
of the body. The whole line has the appearance of being an 
extension of the mass of ganglion cells. This seems the more 
striking as the entire string of cells constituting the rudiment 
of the lateral line in Batrachus seems to occupy the same relative 
position as the extension of ganglionic fibres in Acanthias. 

Wilson (14) states that he has been unable to trace the 
origin of nerves in the Bass. He says in regard to the lateral 
branch of the vagus, that he could not distinguish it " during 
embryonic life " nor " in the larvae of two or three days." 

It is difficult to reconcile Hoffmann's (18) observations on 
Salmo with the facts brought out by Wilson (14) or with the 
conditions existing in Batrachus. That the origin of the sense 
organ rudiment precedes the appearance of the nerve in both 
the Bass and Batrachus can hardly be doubted, while from the 
description of the "growing sensory tissue" in the skin of 
Amia, Allis (2) surely conveys the idea of the early appear- 
ance of the sense organ rudiment. 

3. Formation of canals. — Figs. 7-1 1 represent the appear- 
ance of the head of Batrachus during the period of the 
enclosure of the organs in canals. The plates of Allis show in 
detail the different steps of this process of canal formation, 
and a very full account of the same is to be found in the admi- 
rable paper on the development of the lateral line organs of 
Amia. Previous to this paper, we have the accounts of canal 
formation in Cottus gobio by Bodenstein (9), and in Plateria 
by Schulze (24) and Solger (25), but the illustrations of the 
subject, as well as the accounts, are not so full and clear as in 
the case of Amia. 

The appearance of the head during these stages is almost 
identical in Amia and Batrachus. At the time of hatching, 
the organs are not apparent on the surface, but after treatment 
with picro-sulphuric acid they may be seen below the surface 
as whitish spots or irregular lines (Fig. 6). 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 245 

The canals are formed in sections, as described by Allis (2) : 
"After a developing canal organ has reached the surface, it 
begins to sink, carrying with it the surrounding tissues, thus 
forming a small pit at the bottom of which the organ lies. 
Lips grow upward and inward from the edges of the pit, and 
meeting above the organ, form a short canal, the openings of 
which are inclined to the general surface and give to the canal 
a tunnel-like appearance." In Figs. 7 and 8 the organs have 
begun to sink below the level of the surface and form linear 
areas of depression. 

In Figs. 9, 10, and 11 the process has been continued and 
the organs are partially enclosed by the approaching lips of the 
canal, but complete fusion has not taken place. This condition 
is permanent in some forms, as Chimaera and Polyodon, 
open grooves taking the place of canals in the adult. The 
process of enclosure goes on unequally; the most anterior organs 
are the first to become enclosed. In Fig. 10 the line of fusion 
of the nasal tube is distinctly seen, and the two half pores 
which are formed constitute the anterior and posterior nares. 
In the supraorbital line the process of fusion is carried out 
most completely, the short canals coalescing and therefore no 
primary pores formed, the terminal or half pores only being 
present (Figs. 2 and 23). A comparison of the commissural 
canal between the eyes, so prominent at this stage (Fig. 10), 
with the bony channels on the frontal bones (Fig. 4) is instruc- 
tive, as showing the effect of the flattening of the head and 
the closer approximation relatively of the eyes in the adult. 

In the case of the operculo-mandibular line (Fig. 9) the oper- 
cular portion is seen to form independently of the mandibular 
division, and the double or primary pore which marks their 
union remains larger than the others of the line (Fig. 22). 
In the mandibular portion of the line the four anterior organs 
are never enclosed in a canal, but retain the open groove 
condition in the adult (Fig. 3). 

4. Connecting strand. — While examining adult specimens of 
Batrachus which were partially macerated in nitric acid my 
attention was attracted by a very well-defined strand connecting 
the organs on the side of the body. This structure had the 






; ~:i XV. 



ine~ : : :~ :~. 






set~ 



"irs :: ir. l : 

ells :s :': _- i 




'ir.i :s rtrreftr. 
: :: :~ :.~ t ep: 







.1: :- :*~e 
::." r strand 



c— : - 



ii :i:::y : 
: - :::. : 7. 1 : t ; 



[Fig. 16), as tih 

e : : r i r. 2:::: 



No. 2.] 



LINE SYSTEM OF BATRACHUS TAU. 



247 



Vj-g^r^^T-*- C 



cells, having no connection with the nerve, as suggested by 
Bodenstein, when he speaks of the possibility of its forming 
anastomoses with the nerves in the series of sensory hillocks. 
Emery (26) describes what he calls "epithelial canals" in the 
adult Fierasfer, and 
his figures leave no 
doubt as to their 
homology with the 
connecting strand of 
Batrachus (Cuts 6 
and 7). No mention 
is made of any con- 
necting canals be- 
tween the canal 

organs, but they are evidently well developed between the 
" nerve buttons " (pit organs) of the accessory lines. 

The fact that these "canals" sometimes branch and end 
blindly (Cut 7) is a peculiar characteristic if these canals are 
functional. Exactly similar peculiarities are noticed in the 
case of the strand in Batrachus. The free organs situated in 
a line parallel with the canal on the mandible have the strand 




Cut 6. — Copied from Fig. 58, Emery (26). 



con. St. 




Cut 7. — Copied from Fig. 6, Emery (26). 

directed at right angles to the canal, and in one case the end 
of the cord was branched in a similar way to that figured 
by Emery. In a series of cross-sections the irregular out- 
line of this strand in Batrachus becomes evident (Cut 8). 
There is some indication of its being fibrous in structure, and 




248 CLAP P. [Vol. XV. 

often near the organ a suggestion of a lumen is noticed, 
especially in longitudinal sections. 

According to Leydig (1), Fee (27) seems to have figured this 
connecting strand, but makes no allusion to it. Solger (25) 
refers to the "side organ chains," in the case of Acerina cer- 
nua and Lota vulgaris, and speaks of the chain as consisting 
of "marrowless nerve fibres enclosed in a nucleated sheath." 
Merkel (20) speaks of " modi- 
fied (cutis) epithelium" and 
suggests that the connecting 
strand may be the vestige 
of a canal ! The presence, 
however, of both the canal 
and the connecting strand, 
one found within the other, 

aS in BatrachuS, WOuld OVer- Cut 8. — Cross-sec'titfn of strand between organs 
. , ., . 9 and 10 of infraorbital line of Batrachus. 

throw any such supposition. 

Carriere (28) thinks there is no possibility that this " chain " is 
composed of nerve fibres. Ryder (29) speaks of "faint fila- 
mentous prolongations " from the organs. In a figure of 
Savi's (40) vesicles there is a connecting cord shown and 
described as "filament anastomotique," which suggests the 
same structure. 

Leydig (1) has examined this peculiar structure in Gobio, 
Rhodeus, Salmo, and Anguilla, and although reaching no con- 
clusion as to its significance, says that the strand does not 
consist of nerve elements, but principally of epithelial cells 
which enclose a space that may be considered a lymph passage, 
or, in some cases, no lumen being present, the strand presents a 
fibrous or ligamentous appearance. He regards the "epithelial 
canals" of Fierasfer as lymph channels. Leydig (1) further 
observes that although he has not seen the epithelial thick- 
enings out of which the sense hillocks arise, it is probable that 
the strand is derived from these thickenings. From this point 
of view the strand would be a remnant of an epithelial growth 
which separates from the epidermis and forms the foundation of 
the sense hillocks. Leydig (1) utterly discards the idea that this 
structure is in any way connected with the later forming canaL 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 249 

In regard to the origin of the strand, my observations on 
the embryos and larval forms of Batrachus would tend to con- 
firm the opinion expressed by Leydig. Whatever the function 
may be, its origin from the sense organ rudiment is not to be 
doubted. In very young embryos the growth of the sensory 
tissue is easily demonstrated, as shown elsewhere. In the 
larval fish 15 mm. long, just after the yolk has become 
absorbed, the strand is distinctly seen in preparation of the 
skin, the cells of the strand between the organs still retaining 
much the same appearance as in earlier stages (Fig. 1 5, con.st.). 
Later, however, the cells undergo a change so that the tissue 
appears as seen in Fig. 16, con.st. 

Comparison with Other Teleosts. 

1. Lophius piscatorius. — The goosefish resembles the toad- 
fish in being destitute of scales and in having similar tentacu- 
lar appendages in various parts of the body (Guitel, 30). The 
sense organs are not enclosed in canals, but are protected 
by projections of the skin, as in the case of the free organs 
of Batrachus. The maxillary portion of the infraorbital line of 
organs is greatly developed and the suborbital is wanting. 
The innervation is quite similar in the two forms, the dorsal 
branches of the VII being quite distinct from the V. 

2. Cottus gobio. — Bodenstein (9) has described the " con- 
necting strand " in the adult Cottus and represents it in his 
figures as on the floor of the canals. From his description of 
the skin and the appearance of the canal organs, there is a 
striking similarity between the two forms. 

3. Amiurus. — Batrachus and this common fresh-water form 
have several characteristics in common. The naked skin, 
closely studded with gigantic gland cells, the depressed head, 
and general shape of the body is the same, but the sense organs 
of the trunk in Amiurus are, for the most part, in canals. The 
interesting comparison is in respect to the course of the 
R. dorsalis recurrens facialis, which has been wrongly called 
" trigemini," In Amiurus, according to Wright (31) and Pol- 
lard (32), this arises from a " posterior dorsally placed gangli- 



; : ; _\I.-..-. r y?L 

' - : . : w.:'.':': - : : ' '. . : '. . : .1 " : . : " '-.' ' " ' :. t : 
bone. * and from thence on : : : : : ii m a iaii ng a dorsal line 

:: :ciie mars Tzis :: : is :ri:i::ei_y i:~ :_:i:is ~:b 
the R. recurrens of 1 : :~chns, although taking a ymw tint 
7 ." :tt t ;::i:i inn ire ::;i ::.: _: 
■ :; : t :- 757:: :les " ~ zraiiiis. 

f_ :t connecting strand * is well developed, and 

:ib Ener ;: inscribes rhis =r;cr::r is ir 7; ::ie 1 
e: " : 7 7 7-i ; t .i .11: 11 renins: 7 :r:n us ririres 
: _ : — A : E . - . -■.■.:"..-.•■■". 7 

nan : lie sane ;.::::;:7:i:.i 11: 1 I :::::i_i ".1 :anals 
ire ------ - ' :- eiclosed within lie be res :: :ne =kil_ 1 : : 

is :i tlabrmt i -ten ::' branch _ : 

::i n: i pcres : :e 1 Aliis ; has show* that the 

:rigeri :es i-: ;an . :: lie :anal :rzni 

:: Arna. Tit 1:11:. bids ::ni :i 51:1 1:11:11:7; :i :ne 

;.::::- 7 bead :: Ania ire it: ireser: .1 zainiiis 

f JVAv ;:.;■: j — 7' :::_ :e~tei :ie laieral line cf 

111 I :::::: 1. ;t : :een nait ;: : 

■ ■ 7 . .it: 7 viE ::: : : :e : 111.1 :: tus: .1 ::_: nice 

of origi ::: hn iroops of fishes. So fir ■ 

7 ner.i::cr 7:17: 1:7:7 1 rrea: =:nEar :e:~een 

zi iracris 1.11 seEiiinns Evan :: las i; 1 :ba: :ie 

ine zrrars ire rirrded : 1:7 i:rsal :ran:nes :: 

::_t \TI and X cranial nerves 

" _":. "•?.::,;! — riikis [5 
connecting 11: "."II an: quite prominent in Irrotopterns. 

H: iees 1:: ::: : 

E ending an to the body, but shows its union with the vagus 

gangnnn. This c ommissu re m undoubtedly Imnmfci ^ tmu with 

: R. recunens facialis cf Batxachns. A few of the sense 

organs : itopterus are enclosed in canals, bot they are, for 

the most pan. surface of the body, as in Batrachns. 

jstamtes. — The commssore between the VII and X 
has been found 7 romyzon and figured by Ablborn (5 ; 

nnius _ eaks of the N. lateralis as "formed portly by 
kmmdk from the fmnmh\ fmssimg mmmmd •mix ijrfT r the 

:'::: • . " - \ : . 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 25 1 

in higher forms ." This is a complete description of the course 
of the R. recurrens facialis in Batrachus. 

9. Amphibia. — While Batrachus is a true teleost, there are 
certain superficial resemblances to the Urodeles, the sense 
organs of both having much the same appearance and arrange- 
ment on the body. 

As regards the course of the cranial nerves, Strong (11) 
has pointed out the remarkable homologies that are presented 
in the tadpole and the teleost ; the dorsal branches corre- 
sponding to those of teleosts being present in the tadpole but 
becoming aborted in the adult frog. 

General Summary. 

Development of organs and canals. — The sense organs of the 
lateral system in Batrachus arise from special cords of cells 
formed in the lower layer of the epidermis. These cords origi- 
nate from certain thickenings which make their appearance in 
the auditory region of very young embryos, and proliferate 
along definite lines on the head and trunk. The enlarged 
growing end of one of these cords pushes its way from the 
auditory region to the extreme posterior part of the body, 
the swollen appearance remaining conspicuous for some time 
in the region of the caudal fin. 

These thickenings of the ectoderm give rise to the sense 
organs; each organ arising as a "local proliferation" of cells 
along the cord (Fig. 15). These cells push through the over- 
lying epidermal cells and gradually take on the form and char- 
acter of the adult organ, having the hair cells well developed, 
and the so-called "cupola" structure surmounting the organ. 

In a later stage each organ sinks slightly below the surface, 
and a pointed fold of the skin projects on either side of it. 
This is the permanent condition of the majority of the sense 
organs of Batrachus. On each side of the head, however, four 
short canals are formed. They enclose organs identical with 
those remaining on the surface, and the canals may be regarded 
as a fusion and extension of the paired flaps which serve to 
protect the free organs. In the adult the canals lie in open 



252 CLAP P. [Vol. XV. 

channels of the dermal bones and only primary pores are 
present. 

Innervation. — The dorsal branches of the VII and X cranial 
nerves supply the lateral line system. The supraorbital line 
of organs are innervated by the R. ophthalmicus superfacialis ; 
the infraorbital by the R. buccalis facialis ; the operculo-man- 
dibular by the R. mandibularis externus ; while the vagus sends 
branches to the single canal organ in the temporal region, as 
well as to the organs on the top of the head. 

The anterior organs of the trunk are supplied by the R. re- 
currens of the VII, which forms an anastomosis with a branch of 
the vagus just outside of, and posterior to, the auditory capsule, 
and extends on to the body, occupying a position directly super- 
ficial to the N. lineae lateralis. The R. recurrens in Batrachus 
is probably the same as the R. dorsalis recurrens facialis (tri- 
gemini) of the Siluroids, or of the cutaneous quinti in Gadus, 
although following a different course on the side of the body. 

It remains for future investigation to determine the exact 
innervation of the organs on the body of Batrachus. 

The complexity of the peripheral nervous system grows more 
apparent with every step of advance in methods of investiga- 
tion. In Kupffer's words, " The researches of the last decade 
in comparative embryology have shown that the development 
of the peripheral nervous system is a far more complicated 
process than it was formerly supposed to be" (36). This 
is especially true in the case of the vertebrate head, as the 
recent work on Amphioxus by Hatschek (37), and the important 
investigations by Kupffer (38) on Ammocetes clearly show. 

In the views of Hatschek (37) we encounter a slightly modi- 
fied form of Balfour's hypothesis in regard to the origin of 
both cranial and spinal nerves from a type of segmental nerves 
which had only dorsal, yet mixed dorsal roots. According to 
Hatschek the spinal nerves have lost certain elements, while the 
cranial nerves have retained more of the primitive characteris- 
tics. In Petromyzon, Kupffer (38) has shown that the "dorsal 
spinal nerve root" and the " mixed head nerve root" exist 
together side by side as coordinate components of a typical 
head nerve. 



No. 2.] LINE SYSTEM OF BATRACHUS TAW. 253 

In the researches of Kupffer (36), we gain important addi- 
tions to our knowledge of the development of the cranial 
ganglia in connection with the thickenings of the ectoderm 
which have long been recognized, but little understood. Since 
Beard's (16) and Froriep's (39) simultaneous discovery of " bran- 
chial sense organs " in the embryos of sharks, and the corre- 
sponding transient structures in embryos of higher forms, there 
has been much controversy in regard to the question of the 
ectoblast elements entering secondarily into the formation of 
the cranial ganglia and nerves. There has been much hesita- 
tion on the part of investigators in accepting this fact, for, as 
Froriep (39) has said, " It would certainly bring about a 
fundamental change in our views, were we to be convinced that 
during a long period of embryonic development, the whole 
ectoblast possessed the capacity to act as ' Nervenkeim.' " 

It is now settled beyond dispute that these "placodes" in 
Ammocetes do furnish material to the processes growing down 
from the neural ridge, and subsequently forming the cranial 
ganglia and nerves. The peripheral portion of the "placodes " 
may become the "foundations of the primary sense organs." 
The sense organs of the lateral line, although distributed over 
the entire length of the trunk, are connected with ganglia 
formed in the head region, and are therefore innervated by cranial 
nerves. There seems every reason for considering the system 
as belonging with the more highly specialized sense organs. 

In his admirable paper on "The Cranial Nerves of Am- 
phibia," Strong (11) has shown the extensive modification 
which takes place in the nervous system of Rana, due to the 
disappearance of the lateral line organs in the adult, and sug- 
gests " the importance of taking into full consideration, as a 
factor, the cutaneous sense organs in the attempt to obtain a 
philosophical understanding of the changes undergone by the 
peripheral and central nervous systems. The development 
and specialization of these structures have probably played an 
important part in the changes leading to the organization of 
the vertebrate peripheral and central nervous systems." 

University of Chicago, 
May, 1896. 



254 



CLAP P. 



[Vol. XV. 



BIBLIOGRAPHY. 



10. 



17. 
16. 



33. Ahlborn, F. Ueber den Ursprung und Austritt der Hirnnerven von 
Petromyzon. Zeit.f. wiss. Zool. Bd. xl. 1884. 
2. Allis, Edward Phelps, Jr. The Anatomy and Development of 
the Lateral Line System in Amiacalva. Journ. of Morfih. Vol. ii, 
No. 3. 1889. 
Ayers, Howard. Vertebrate Cephalogenesis. II. A Contribution 
to the Morphology of the Vertebrate Ear, with a Reconsideration of 
its Functions. Journ. of Morph. Vol. vi, No. 1. 1892. 
Balfour, F. M. Elasmobranch Fishes. 1877. 
Beard, John. The System of Branchial Sense-Organs and their 
Associated Ganglia in Ichthyopsida. Q.J. M. S. Vol. xxvi, n.s., 
No. 101. 1885. 
9. Bodenstein, Emil. Der Seitenkanal. von Cottus gobio. Zeit. f. 
wiss. Zool. Bd. xxxvii, Heft 1. 1882. 
28. Carriere, G. Postembryonale Entwicklung der Epidermis des 
Siredon pisciformis. Arch. mikr. Anat. 1884. 

6. Collinge, W. E. The Sensory Canal System of Fishes. Part I. 

Ganoidei. Q.J. M. S. Vol. xxxvi, n. s. 1894. 

26. Emery, C. Le Specie del Genere Fieras nei Golfo di Napoli e 

Regimi limitrofe. Fauna und Flora des Golfes von Neafiel. II. 
Monographic 1880. 
12. Ewart, J. C. The Lateral Sense-Organs of Elasmobranchs. I. 
The Sensory Canals of Laemargus. II. The Sensory Canals of the 
Common Skate (Raia batis). Trans. Roy. Soc. Edinb. Vol. xxxvi, 
Part 1. 1892. 

27. Fee. Recherches sur le nerf pneumo-gastriquechezlespoissons. 1869. 
39. Froriep, August. Entwicklungsgeschichte des Kopfes. Merkel 

und Bonnefs Anat. Hefte. Bd. i. 1891. 
5. Goode, G. Brown. Natural History of Useful and Aquatic Animals. 

1884. 
21. Gotte, Alexander. Die Entwicklungsgeschichte der Unke. 1875. 
30. Guitel, F. Recherches sur la ligne laterale de la Bandroie (Lophius 

piscatorius). Arch, de Zool. ex. et Gen. Ser. 2. Tome ix. 1881. 
37. Hatschek. Die Metamerie des Amphioxus und des Ammocoetes. 

Verh. d. anat. Gesell., Sechste Versammlung. 1892. 
18. Hoffmann, C. K. Zur Ontogenie der Knochenfische. Arch, f 

mikr. Anat. Bd. xxviii, Heft 1. 1883. 
4. Jordan and Gilbert. Synopsis of the Fishes of North America. 

Bull. U.S. Nat. Mus. No. 16. 1883. 

7. Kingsbury, B. F. The Lateral Line System of Sense-Organs in 

Some American Amphibia and Comparison with the Dipnoans. 
Proc. Am. Micr. Soc. Vol. xvii. 1895. 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 255 

36. Kupffer, C. von. Entwicklungsgeschichte des Kopfes. Merkel 
und Bonnet's A?iat. Hefte. Bd. ii. 1892. 

38. Kupffer, C. von. Studien zur vergleichenden Entwicklungsge- 
schichte des Kopfes der Kranioten. Heft 2. Die Entwicklung 
des Kopfes von Ammocoetes Planeri. Miinchen und Leipzig. 1894. 
1. Leydig, F. Integument und Hautsinnesorgane der Knochenfische. 

Weitere Beitrage. Zool. Jahrb. Bd. viii, Heft 1. 1894. 
8. Leydig, F. Zur Anatomie und Histologic der Chimaera monstrosa. 
Miiller's Archiv f. Anat. u. Phys. 1851. 

20. Merkel, Fr. Ueber die Endigungen der Sensiblen Nerven in der 
Haut der Wirbelthiere. Rostock. 1880. 

15. Mitrophanow, Paul. Etude embryogenique sur les Selaciens. 
Arch, de Zool. ex. et Gen. Ser. 3. Tome i. 1893. 

13. Pinkus, F. Die Hirnnerven des Protopterus annecteus. SchwalbVs 

Morph. Arbeiten. Bd. iv, Heft 2. 1894. 
19. Platt, J. B. Differentiations of Ectoderm in Necturus. Q.J. M. S. 

Vol. xxxviii, Part 4. 1896. 
32. Pollard, H. B. The Lateral Line System in Siluroids. Zool. Jahrb. 

Bd. v. 1892. 
3. Ryder, John A. A Preliminary Notice of the Development of the 

Toadfish (Batrachus tau).- Bull, oj U.S. Fish Comm. 1886. 
29. Ryder, John A. Embryography of Osseous Fishes. Report of 

U. S. Fish Comm. for 1882. 
40. Savi, Paul. D'etudes anatomiques sur le systeme nerveux et sur 

l'organe electrique de la Torpillo. 

24. Schulze, Franz Eilhard. Ueber die Sinnesorgane der Seitenlinie 

bei Fischen und Amphibien. Arch. f. mikr. A?iat. Bd. vi. 1870. 

22. Semper. Merkel und Bonnet" 1 s Anat. Hefte. Bd. i, p. 592. 1891. 

25. Solger, B. Neue Untersuchungen zur Anatomie der Seitenorgane 

der Fische. Arch, f mik. Anat. Bd. xvii, Heft 1, iv, and Bd. xvii, 
Heft 3. 

34. Stannius, H. Das peripherische Nervensystem der Fische, anato- 
misch und physiologisch untersucht. Rostock. 1849. 

11. Strong, Oliver S. The Cranial Nerves of Amphibia. A Contri- 
bution to the Morphology of the Vertebrate Nervous System. Journ. 
of Morph. Vol. x. 1895. 

23. Van Wijhe, J. W. Ueber die Mesodermsegmente und die Entwick- 

lung der Nerven des Selachierkopfes. 1882. 

14. Wilson, H. V. The Embryology of the Sea Bass (Serranus atra- 

rius). Bull, of U.S. Fish Comm. Vol. ix. 1891. 
31. Wright, R. Ramsay. On the Nervous System and Sense-Organs 
of Amiurus. Proc. Can. Inst. Vol. ii, Fasc. No. 3. Toronto. 1884. 



256 CLAP P. [Vol. XV 



REFERENCE LETTERS. 

A. = anal fin. 
ac.b. = accessory membrane bone. 
ac.md.l. = accessory mandibular line. 

a.l. = anterior pit line of head (Amia). 
an.r. = anterior root. 
an.na. = anterior nasal aperture. 

ar.= articular. 
buc.f. = ramus buccalis facialis. 

cb. = cerebellum. 
C.H. = cerebral hemispheres. 
c.l.= cheek line 
com. VII-X = commissure between VII and X. 
con.st. = connecting strand. 
d. = dentary. 
d.b. VII = dorsal branch of VII nerve. 
d.b.ll.n. = dorsal branch of nervus lineae lateralis. 
d.b.recf. = dorsal branch of recurrens facialis. 
d.l. = dorsal line. 
d.o.l. = dorsal opercular line. 

ep. = epiphysis. 
F.R. = frontal. 
f.g. = facial ganglion. 
g.l. = glossopharyngeal nerve (Amia). 
g.g. = Gasserian ganglion. 
h.l. = horizontal pit line of cheek (Amia). 
1. 0. C = infraorbital canal (Amia). 
II. r. = lateral line rudiment. 
vi. = muscles. 
MX.C = maxillary canal. 
md.L = mandibular line. 

m .e.f. — ramus mandibularis externus facialis. 
m.l. = middle dorsal pit line of head. 
n.ll. = nervus lineae lateralis. 
n.c. = noto chord. 
ocf. = supraoccipital foramen. 
oil. = olfactory lobes. 
OM. C. = operculo-mandibular canal. 
OP. = operculum. 

op.f. = ramus ophthalmicus superfacialis. 
op.l. — optic lobes. 
O.S. = opercular spine. 
ot.n. = otic nerve (Amia). 
p. = pore of canal. 
P. = pectoral fin. 
pigm. = pigment. 

pi. = posterior pit line of head (Amia). 



No. 2.] LINE SYSTEM OF BATRACHUS TAU. 257 

p.n.a. = posterior nasal aperture. 
P.OP. = preoperculum. 
p.r. = posterior root. 
reef. = ramus recurrens facialis. 
s.or. = sense organ. 
SO.C. = supraorbital canal. 

sp.c. = spinal cord. 
st.com. = supratemporal cross-commissure. 
stv' . = supratemporal branch of vagus. 
T.A. = tuberculum acusticum. 
T.C = temporal canal. 
V. = ventral fin. 
v.b.rec.f. = ventral branch of recurrens facialis. 
v.o.l. = ventral opercular line. 
v.g. = vagus ganglion. 
z/.2 — second branch of vagus. 
•wd. = wolffian duct. 



: ; : CLAa 



EXPLANATION OF PLATE XVIL 

Fig. i. Side view of head of Batrachns tan, one year old. X 6. Showing 
the appearance of the lines of sense organs in the adult, also the position of the 
paired flaps and other projections of the skin on the head. 

Fig. 2. Dorsal view of same, x 6. 

Fig. 3. Ventral view of same. X 6. 

Fig. 4. Dorsal view of skoIL Natural size. 

Fig. 5. Ventral view of mandible. Natural size. The grooves show the 
position of the lateral line organs. 

In F%. 4, iot/R read FR. 



Journal of Morphology Vol. XV. 




260 CLAP P. 



EXPLANATION OF PLATE XVIII. 

Fig. 6. Embryo of Batrachus at time of hatching, showing the different lines 
of organs well defined. X 15. 

Fig. 7. Side view of head of larva, showing sense organs on the surface. X 6. 

Fig. 8. Front view of same. 

Fig. 9. Side view of head, a few days later, showing canals in process of 
formation. X 6. 

Fig. 10. Front view of same. 

Fig. 11. Dorsal view of same. 

Fig. 12. Dorsal view of brain, showing roots of cranial nerves. X 6. 

Fig. 13. Diagram showing connections between the VII and X. The intra- 
cranial commissure, and the anastomosis of the recurrens facialis with a branch 
from the X. The VIII has been omitted, as also the portion of the X innervating 
the branchial region. 



Journal <>/'J/nr/>//, •/<>,/// !',>/. \i 




262 CLAP P. 



EXPLANATION OF PLATE XIX. 

Fig. 14. A horizontal section of an Acanthias embryo 17 mm. long, showing 
the growing point of the lateral line with its "pocket" and the nerve. Cam. 
Z. 16, oc. 3. 

Fig. 15. Drawn from a preparation of the skin, showing the appearance of 
the cells of the organs at an early stage of their development. Cam. Z. 4, oc. 3. 

Fig. 16. A vertical section through a sense organ, showing the relation of the 
connecting strand to the organ. Cam. Leitz 7, oc. 3. 

Fig. 17. Preparation of skin showing the appearance of the rudiment of the 
lateral line organs with its enlarged growing end. Cam. Z. 4, oc. 3. 

Fig. 18. A horizontal section of an embryo of Batrachus 7 mm. long, show- 
ing the position of the growing point of the line in its relation to the outer layer 
of ectoderm and to the muscles. Cam. Z. 16, oc. 3. 

Fig. 19. View of same magnified. Cam. Z. 4, oc. 3. 

Fig. 20. Cross-section through the enlarged portion of the line. Cam. Leitz 
7, oc. 3. 

In Fig. 16, for m read n. 



Journal of Morphology Vbl.XV. 


















' 



«, ,«>>r 



X 



§9 *«j e x 



W £0 - 






264 CLAP P. 



EXPLANATION OF PLATE XX. 

Fig. 21. Diagram showing the innervation of the lateral line organs of Amia. 
Journ. of Morph., Vol. ii, No. 3, PI. XLII (reduced). 

Fig. 22. Diagram showing innervation of the lateral line organs of Batrachus. 
The lines in blue indicate the sense organ with the connecting strand. 

Fig. 23. Diagram showing dorsal view of the same. The course of the nerves 
is shown on the right, and the position of the connecting strand, in blue, on 
the left. The short lines on each side of the organ represent the position of the 
paired flaps. 

Fig. 24. View of left side of body of Batrachus one year old. Showing posi- 
tion of sense organs in adult. Natural size. 

In Fig. 21, for st.cbm. read st.com. 

In Fig. 22, in supraorbital line, supply 1, 2, 3, 4, 5, 6, as indicating the organs 
of that line. 

For d.b.nec.f. read d.b.recf. 
For b.n.ll. read db.n.ll. 



Journal of Morphology Vol. XI 



IX KC.fAl.Mcf ,11 







J 



o 1901 



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